Digital systems are being developed for use with voice communication applications. Typical digital voice systems in the past have relied on encoding techniques which require high data transmission rates to achive an acceptable quality of voice. Because of the tremendous amount of information required to represent a voice signal, some systems require large memories if a digital voice signal is to be stored for later use. One voice encoding technique is referred to as CVSD and it provides good quality of voice but at the expense of a large amount of data at a high data rate. LPC speech encoding is by far the most efficient technique for digitally encoding speech, and offers considerable advantages over CVSD and other techniques. It is well known in the art that the quality of LPC encoded and decoded voice signals can be improved by transmitting the LPC parameters at a higher bit rate. Present technology gives good voice quality for LPC parameter encoding at 2400 bits per second, and excellent speech quality when clock rates of 4800 bits per second (or more) are used.
Now, typical paging systems are lightly loaded during the off-hours, from 6 PM to 8 AM, and become fully loaded during the peak hours of 9 AM to 4 PM.
It is desirable and possible to use 2400 BPS LPC encoding in conjunction with 12000 BPS digital modulation to achieve good voice quality of a high system message throughput during the busy hours of the day. The use of this LPC compression technique would give the system roughly five times the throughput during the peak load periods.
However, during the off-hours when the system is not fully loaded, the five to one throughput improvement is not needed, and it is desirable to use a higher LPC data rate to obtain improved voice message quality. Alternatively, it is also desirable to use different LPC bit rates to provide different voice quality levels for different tariffs. Thus, this invention provides a system and paging receiver in which the LPC analysis generates data at different bit rates (for example, 2400 BPS and 4800 BPS), transmits the data at an accelerated bit rate (for example, 12K BPS), and provides different levels of voice quality at the receiver.